Abstract: A process for producing a prepreg resin composition includes mixing 100 parts by weight of solid acrylonitrile butadiene rubber with 50 to 400 parts by weight of a solid epoxy resin having a melting point or softening point of 40° C. or higher at a temperature lower than the melting point or softening point of the solid epoxy resin in the absence of a solvent to form a pre-mixture, and mixing the pre-mixture with 500 to 7,000 parts by weight of a liquid epoxy resin having a melting point or softening point of lower than 40° C. and 0.6 to 1.1 equivalents of an aromatic amine-based curing agent based on the epoxy groups which belong to the solid epoxy resin and the liquid epoxy resin. The solid rubber component can be uniformly dispersed in the epoxy resin without using a solvent.